The invention relates to methods of corn milling and efficiently separating degerminated corn into endosperm and germ fraction output streams. More particularly, the present invention relates to a method of separating degerminated corn using a table separator where the degerminated corn comprises endosperm and germ and has had the hull substantially removed, the degerminated corn being separated on the basis of density into at least two output streams comprising at least one endosperm-rich fraction output stream and at least one germ-rich fraction output stream. The invention also, more particularly, relates to a method of milling corn that incorporates the aforementioned, inventive separation process.
The present invention also relates to a table separator used in the separation process in both inventive methods. More particularly, the invention relates to a table separator suitable for separating degerminated corn into at least one endosperm (grit) fraction output stream having a relatively high concentration of endosperm and at least one germ fraction having a relatively high concentration of germ, wherein the solid surface of oscillating trays used in the table separator have a plurality of surface dimples or indentations of a specified depth and shape in a linear array for facilitating the separation process.
Generally, corn milling processes for the production of grits and other corn products separate the endosperm from the germ and the hull. In white corn used for grit production, the endosperm typically accounts for approximately 80-85.5 on a weight basis of the corn kernel whereas the germ and the hull respectively account for approximately 10-14% and 5-6%. The germ is substantially high in fat, typically containing approximately from 31.1% to 35.1% fat on a dry weight basis. Production of various types of corn products requires that the grit be separated from the germ. The germ is useful for recovery of corn oil because of its relatively high fat content. In addition, even a relatively small amount of fat remaining in the grit can cause such grit to become rancid, impart a mealy texture to a cooked grit product or impart other undesirable qualities to foods containing such product.
Conventionally, after corn has been degerminated (i.e., fractured into pieces of endosperm (grit) and germ), the endosperm is separated from the germ by means of vacuum gravity separators, also termed xe2x80x9cgravity tables.xe2x80x9d Gravity tables include, for example, pneumatic concentrators. These devices have a porous table surface on which the material to be separated is fed. As air is forced through the pores, it fluidizes the material, causing the particles of the material to move across the table surface based on density, size, and shape. Changes in slope of the table can be used to further improve the degree of particle separation. These systems, however, take up considerable space in the production facility and are not only relatively costly to purchase but also relatively expensive to operate as they require large volumes of air, in the range of about 4,000-5,000 CFM to process about 83 pounds of corn per minute. Further, during the course of the separation process, vacuum gravity systems require substantial dust collection and handling equipment, adding further to the capital and operating cost of such systems.
Consequently, there exists a need for a less expensive and more efficient system and method for separating the endosperm from the germ which requires less space in the processing facility. There also exists a need for a method of corn processing that incorporates the aforementioned method of separating the endosperm from the germ.
In accordance with one aspect of the present invention, a corn milling system and method is provided for efficiently separating degerminated corn into endosperm and germ fractions on the basis of density by use of a table separator. It was discovered unexpectedly that table separators, typically used for separating objects of regular and/or uniform shape such as rice grains, could be effectively used in a process for separating degerminated corn, which degerminated corn consists of relatively randomly and irregularly shaped pieces of corn endosperm and germ after fracturing in a degerminator. The method involves (a) supplying a feed stream of degerminated corn to the table separator and (b) separating the degerminated corn so as to form at least two output streams comprising at least one endosperm fraction output stream having a predominant concentration of endosperm (grit) and at least one germ fraction output stream having a predominant concentration of germ. Preferably, the table separator is operated so that the output stream containing primarily endosperm fraction typically has, on a weight basis, a minimum concentration of 90% endosperm with the balance being corn germ, and the output stream containing primarily corn germ fraction typically has a minimum concentration of 90% corn germ with the balance being endosperm. Generally, in commercial production, steps (a) and (b) will occur continuously, although the method may be practiced on a batch basis.
As used herein, the term xe2x80x9ctable separatorsxe2x80x9d refers to a separator having a solid table or solid tray-like surface on which separation of corn endosperm and germ is achieved by feeding the corn endosperm and germ onto the table or tray-like surface and oscillating or reciprocating the surface to effect a separation of endosperm and germ based on density differences. There are two principal types of table separators: oscillating tray separators and compartment separators. In both types, the degerminated corn is fed onto a solid table or tray-like surface that is subjected to oscillating or reciprocating movement which causes the degerminated corn to separate into fractions of endosperm and germ.
As used herein, the term xe2x80x9cdegerminated cornxe2x80x9d refers to corn kernels that have been fractured to release their constituents, comprising endosperm, germ, and hull. Usually, the hull component is substantially removed before separation of the endosperm and germ components by any suitable means known to those skilled in the art, such as an aspirator, for example.
In accordance with another aspect of the present invention, a corn milling process is provided which incorporates the foregoing method for separating the endosperm from the germ. The corn milling process comprises degerminating (fracturing) the corn kernels into germ and endosperm pieces or particles, and thereafter separating the endosperm particles from the germ particles with a table separator to form at least one endosperm fraction output stream having a relatively high concentration of endosperm and at least one germ fraction output stream having a relatively high concentration of corn germ.
In accordance with another aspect of the invention, a table separator is provided that is particularly useful for practicing the foregoing disclosed methods of corn milling and separating degerminated corn. The table separator has at least one, and may have a plurality of, solid-bottomed trays, positioned so that one side is inclined with respect to the opposite side. The tray or trays oscillate directionally upward and toward the top of the incline, which movement causes an input stream of degerminated corn fed to the table separator to separate into output streams of endosperm and germ fractions.
Each tray has a dimpled or indented tray surface in which the surface of the trays has a plurality of dimples or indentations which facilitate the separation of degerminated corn into fractions on the basis of density. Each dimple is a depression in the tray surface having a depth and a cross-sectional shape and dimension, defined by the dimple perimeter. Preferably, all of the dimples in the tray are of a similar size and shape. Preferably, the dimples have one straight end, a curved end opposite from the straight end; parallel or generally parallel sides; a length typically of about 10-14 millimeters, preferably 11 millimeters; a width of about 5-8 millimeters, preferably 6 millimeters; and a depth that increases from about zero (0) millimeters at the curved end to a maximum working depth in the range of about 1.5 millimeters to about 6.0 millimeters at the straight end, relative to the undimpled portion of the tray surface. The dimples have a side-to-side spacing of about 2 to 4 millimeters and an end-to-end spacing of about 2 to 4 millimeters. Usually, adjacent rows are staggered in the lengthwise direction. Alternatively, the dimples or indentations may be of virtually any shape; for example, round, square, octagonal, or triangular.
Both inventive methods of corn milling and of separating degerminated corn offer numerous commercial advantages over conventional milling techniques, including a higher capacity throughput, a higher degree of separation, a lower operating cost because of reduced requirements for process air, and substantially lower capital equipment costs. Moreover, both inventive methods utilize table separators that take up less space in the production facility and are relatively dust-free in their operation. In addition, the dimpled configuration of the inventive table separator facilitates a higher degree of separation of degerminated corn.